A note on D-brane Interactions in the IIA Plane-Wave Background

We compute the D-brane tensions in the type IIA plane-wave background by comparing the interaction potential between widely separated D-branes in string theory with the supergravity mode exchange between the D-branes. We found that the D-brane tensions and RR charges in the plane-wave background are the same as those in the flat space. Also we work out the stringy halo behavior of the $DpD\bar{p}$ spacelike branes and find the explicit dependence on the light cone separation $r^+$. This suggests that the detailed tachyon dynamics for the spacelike $DpD\bar{p}$ branes are different from those in the flat space case. We also discuss specific features of the exchange amplitudes in relation to the geometric properties of the IIA plane wave background. When branes are located at focal points, full or partial restoration of the translation invariance occurs and the amplitudes are similar to those in the flat space.Comment: 19 pages; discussions on the integrated amplitudes in geometric terms adde

Holography and Infrared Conformality in Two Dimensions

This is a very brief review of some results from hep-th/0112154 and hep-th/0209191. In holographic renormalization, we studied the RG flow of a 2d N=(4,4) CFT perturbed by a relevant operator, flowing to a conformal fixed point in the IR. Here, the supergravity dual is displayed, and the computation of correlators is discussed. The sample stress-energy correlator given here provides an opportunity to explicitly compare Zamolodchikov's C-function to the proposal for a "holographic C-function".Comment: 4 pages, 1 figure, using cargese.cls (included). Proceedings of Cargese ASI, "Progress in String, Field and Particle Theory", June-July 200

Weyl anomaly for Wilson surfaces

We consider a free two-form in six dimensions and calculate the conformal anomaly associated with a Wilson surface observable.Comment: 8 page

Robinson-Trautman spacetimes and gauge/gravity duality

We study far-from-equilibrium field theory dynamics using gauge/gravity duality applied to the Robinson-Trautman (RT) class of spacetimes and we present a number of new results. First, we assess the applicability of the hydrodynamic approximation to inhomogeneous plasma dynamics dual to RT spacetimes. We prove that to any order in a late time expansion it is possible to identify variables corresponding to the local energy density and fluid velocity. However, we show using numerical examples that this does not hold at the non-perturbative level; for sufficiently inhomogeneous initial data a local rest frame does not exist. Second, we preset a new class of holographic inhomogeneous plasma flows on the plane. The corresponding spacetimes are not of the RT type but they can be obtained from RT spacetimes with spatially compact boundaries by coordinate transformations which generate Poincar\'e patch-like coordinates with planar boundaries. We demonstrate the application of this procedure using numerical examples.Comment: Proceedings prepared for the "Workshop on Geometry and Physics" in memoriam of Ioannis Bakas, November 2016, Ringberg Castle, Germany. v2: Minor changes, added discussion of isotropisation tim

Observational signatures of holographic models of inflation

We discuss the phenomenology of recently proposed holographic models of inflation, in which the very early universe is non-geometric and is described by a dual three-dimensional quantum field theory (QFT). We analyze models determined by a specific class of dual QFTs and show that they have the following universal properties: (i) they have a nearly scale invariant spectrum of small amplitude primordial fluctuations, (ii) the scalar spectral index runs as alpha_s = -(n_s-1), (iii) the three-point function of primordial scalar perturbations is of exactly the factorizable equilateral form with f_nl^eq=5/36. These properties hold irrespective of the details (e.g. field content, strength of interactions, etc.) of the dual QFT within the class of theories we analyze. The ratio of tensors-to-scalars is determined by the field content of the dual QFT and does not satisfy the slow-roll consistency relations. Observations from the Planck satellite should be able to confirm or exclude these models.Comment: 4 pp, 2 fig

The Holographic Weyl anomaly

We calculate the Weyl anomaly for conformal field theories that can be described via the adS/CFT correspondence. This entails regularizing the gravitational part of the corresponding supergravity action in a manner consistent with general covariance. Up to a constant, the anomaly only depends on the dimension d of the manifold on which the conformal field theory is defined. We present concrete expressions for the anomaly in the physically relevant cases d = 2, 4 and 6. In d = 2 we find for the central charge c = 3 l/ 2 G_N in agreement with considerations based on the asymptotic symmetry algebra of adS_3. In d = 4 the anomaly agrees precisely with that of the corresponding N = 4 superconformal SU(N) gauge theory. The result in d = 6 provides new information for the (0, 2) theory, since its Weyl anomaly has not been computed previously. The anomaly in this case grows as N^3, where N is the number of coincident M5 branes, and it vanishes for a Ricci-flat background.Comment: 12 pages, Latex, v2: minor improvement

Non-equilibrium dynamics and AdS4AdS_4 Robinson-Trautman

The Robinson-Trautman space-times provide solutions of Einstein's equations with negative cosmological constant, which settle to $AdS_4$ Schwarzschild black hole at late times. Via gauge/gravity duality they should describe a system out of equilibrium that evolves towards thermalization. We show that the area of the past apparent horizon of these space-times satisfies a generalized Penrose inequality and we formulate as well as provide evidence for a suitable generalization of Thorne's hoop conjecture. We also compute the holographic energy-momentum tensor and deduce its late time behavior. It turns out that the complete non-equilibrium process on the boundary is governed by Calabi's flow on $S^2$. Upon linearization, only special modes that arise as supersymmetric zero energy states of an associated supersymmetric quantum mechanics problem contribute to the solution. We find that each pole of radiation has an effective viscosity given by the eigenvalues of the Laplace operator on $S^2$ and there is an apparent violation of the KSS bound on $\eta / s$ for the low lying harmonics of large $AdS_4$ black holes. These modes, however, do not satisfy Dirichlet boundary conditions, they are out-going and they do not appear to have a Kruskal extension across the future horizon ${\cal H}^+$.Comment: 48 pages, 2 figures, v2: new section on entropy current, refs added, JHEP versio

Microscopic derivation of the Bekenstein-Hawking entropy formula for non-extremal black holes

We derive the Bekenstein-Hawking entropy formula for four and five dimensional non-supersymmetric black holes (which include the Schwarzchild ones) by counting microscopic states. This is achieved by first showing that these black holes are U-dual to the three-dimensional black hole of Banados-Teitelboim-Zanelli and then counting microscopic states of the latter following Carlip's approach. Higher than five dimensional black holes are also considered. We discuss the connection of our approach to the D-brane picture.Comment: Misprints corrected, discussion section expanded, some references added. Version to appear in Nucl. Phys. B. 29 pages, late